When trying to access the webserver, I get "Internal Server Error unititialized constant Rack::Handler::WEBrick::QUERY_STRING WEBrick/1.3.1 (Ruby/2.2.3/2015-08018) Open SSL/1.0.2d at 127.0.0.1:3004"

I've run the test, and it's missing gems, which fail to install.

Any thoughts?